1. Field of the Invention:
The present invention generally relates to a device for vacuum sealing various containers including plastic bags and canisters, and in particular to a device including a vacuum sensor system for sensing and controlling the evacuation of fluid from a container to a predetermined pressure independent of surrounding atmospheric conditions or container size.
2. Description of Related Art:
Various systems and methods are known for the purpose of vacuum sealing containers to protect perishables provided therein against oxidation. As oxygen is a main cause of food spoilage, removing the air that surrounds foodstuff inhibits growth of bacteria, mold, and yeast. In this regard, vacuum sealed foods often last three to five times longer than normal refrigerated food stored in ordinary containers. Moreover, vacuum sealing is useful for storing all kinds of items such as clothes, photographs or silver in order to prevent discoloration, corroding, rust, and tarnishing. Vacuum sealing also results in tight, strong and compact packages thereby reducing the bulk of supplies and allowing for more space to store food or other articles. Furthermore, vacuum sealing minimizes odors which may spread to other stored items, and also acts to prevent freezer bum.
One type of vacuum sealing system, primarily used for commercial packaging purposes, includes a vacuum chamber in which the entire packaged product is placed, along with heat sealers for sealing the package once a vacuum has been substantially established within the interior of the package. Conventional devices of this type tend to be large, expensive, and stationarily mounted such that the containers to be sealed must be brought to the vacuum packaging device.
Still another type of conventional vacuum sealing system is manufactured to be more compact and economical for home use. One such system is disclosed in applicant's U.S. Pat. No. 4,941,310, entitled, "APPARATUS FOR VACUUM SEALING PLASTIC BAGS", which in one embodiment discloses a vacuum chamber including an opening defined by a stationary support member and a moveable hood. An open end of a container such as a plastic bag to be sealed is received within the vacuum chamber between the support member and the moveable hood, such that when the hood is moved to a closed position, a sealed environment including the vacuum chamber and the interior of the plastic bag is established. A preferred type of bag for use with such a system is disclosed in applicant's U.S. Pat. No. 4,756,422, entitled, "PLASTIC BAG FOR VACUUM SEALING", which plastic bag is provided with a series of air channels on interior surfaces of the bag. The air channels prevent a front section of the bag (i.e., that proximate to the vacuum packaging device) from becoming sealed while there are still air pockets toward a rear of the bag.
After the moveable hood is located in the closed position with the open end of the plastic bag located within the vacuum chamber, a pump within the device evacuates the fluid from within the bag. Once a vacuum is substantially established within the bag, a heat source seals the opening of the bag thereby vacuum sealing the perishable goods within the bag. In order to seal canisters, U.S. Pat. No. 4,941,310 alternatively discloses a vacuum device including a plastic vacuum tube having a first end sealably connected to the vacuum chamber and a second end sealably connected to a canister having a lid customized to receive the second end of the vacuum tube. As in the embodiments of the device for evacuating plastic bags, once the device is turned on, air will be drawn from the canister through the tube by the evacuation pump, until the sensor system indicates that the proper evacuation pressure has been established within the cansiter.
In vacuum packaging devices, it is desirable to evacuate the air from within a container (plastic bag or canister) down to a controlled and repeatable target shutoff pressure, regardless of the surrounding atmospheric conditions. Conventional vacuum packaging devices for vacuum packaging perishable items such as those described above attempt to accomplish this manually or by having a control system turn off the evacuation pump when a vacuum sensor determines that the pressure within the container being evacuated reaches some target fraction of the surrounding atmospheric pressure. A problem with conventional systems, however, is that atmospheric pressure will vary significantly depending on weather conditions and the height above sea level. Consequently, the target shutoff pressure within the chamber will vary as well.
Variance in the desired target pressure presents problems in addition to the lack of precise control and repeatability. For example, if a control system were configured at sea level to shut off the evacuation pump when the pressure sensor measured a chamber pressure of 15% of atmospheric pressure, at higher elevations/low pressure conditions, the pump motor capacity may not be sufficient to evacuate the chamber to 15% of the low pressure surrounding atmosphere. In such an instance, the pressure within the chamber would never reach the fractional target pressure, and the control system would never send the shutoff signal to the pump motor. This would be true even though the absolute pressure within the chamber may have reached or exceeded the intended vacuum packaging level.
The above-described problem may be solved by providing a conservative pump shutoff point, one where the chamber pressure reaches a somewhat larger fraction of the surrounding atmospheric pressure (e.g., 25% of atmospheric). However, this solution presents another problem in that, at lower elevations/higher pressures, the target pressure will be reached when there is still a relatively large amount of air remaining in the chamber. This may provide poor food storage conditions and largely negate the advantages of vacuum packaging.
Many solutions have been offered to deal with the variance in atmospheric pressures at different elevations. A vacuum packaging device is known where a user makes adjustments to the device depending on the surrounding atmospheric pressure. However, this design is not practical or user-friendly because the device would require the user to make frequent adjustments to the reference pressure to operate reliably. Moreover, the precision of these devices depends in part on the user's knowledge of the atmospheric conditions in the area in which the vacuum packaging device is being used. Precise information in this regard is not often readily available.
Another problem with conventional vacuum sealing systems is that such systems typically utilize sensors that measure pressure only indirectly. For example, in U.S. Pat. No. 5,195,427, entitled, "SUCTION DEVICE TO CREATE A VACUUM IN CONTAINERS", the vacuum packaging apparatus includes a pump for evacuating the container, a motor for driving the pump and an electronic vacuum sensor which senses the formation of a vacuum within the container based on the increase in current drawn by the motor. The shortcoming to such an apparatus is that the current drawn will not only depend on the pressure within the container, but also on pump and motor characteristics, which may vary from pump to pump and motor to motor. For example, at low pressures within the container, leakage may occur in the pump, which will result in a different current draw from the motor than should be indicated for the low pressure within the container.
A still further problem found in conventional vacuum packaging systems is that such systems attempt to measure pressure at the target shutoff pressure and near the pump's performance limits, which measurement governs whether or not the pump gets shut off. For various reasons in addition to those described above relating to operation at low ambient pressures, the sensor may never sense the shutoff pressure. For example, the pump may be old or otherwise not operating to its specifications, or there may be a small leak in the container. In these instances, the target shutoff pressure would never be reached and the pump would continue to run.